This invention relates in general to vehicle suspension systems and in particular to an integrated control unit for an active roll control system.
Vehicle suspension systems control chassis motion during operation of the vehicle in order to isolate the vehicle load from irregularities in the terrain over which the vehicle travels. One such chassis motion, that is controlled by know suspension systems, is chassis roll. A vehicle experiences chassis roll during a turning maneuver. During chassis roll, the chassis tilts or “rolls” about the vehicle's fore-to-aft axis toward an outside direction of the turn.
In the past, vehicles have been provided with passive suspension systems that normally include a spring and damper connected between sprung and unsprung portions of the vehicle. Accordingly, a spring and damper is typically provided for each vehicle wheel. Passive suspension systems are generally self-contained and only react to loads applied to them.
More recently, active suspension systems have been developed that apply positive reactions to applied loads. Active suspension systems typically include hydraulic or pneumatic actuators that are coupled to the passive suspension system components. A typical prior art active suspension system with a roll control system 10 is illustrated in FIG. 1. The roll control system 10 includes an Electronic Control Unit (ECU) 12 that is in electrical communication with at least one wheel speed sensor 14, a lateral accelerometer 16 and a steering angle detector 18 that together provide a means for sensing forces that cause the vehicle to roll. The roll control system 10 also includes a front anti-roll bar 20 and a front cylinder and piston assembly 22 associated with the vehicle front wheels 24. Similarly, a rear anti-roll bar 25 and a rear cylinder and piston assembly 26 are associated with the rear wheels 28. The front and rear anti-roll bars 20 and 25 are connected to the vehicle body (not shown) and, via the front and rear cylinder and piston assemblies 22 and 26 and a strut 30a, or via a strut 30b, to the vehicle wheels at pairs of suspension arms 24a and 28a associated with the front and rear wheels 24 and 28, respectively. A pump 32 has an intake port connected by a first hydraulic line to a fluid reservoir 34 and a discharge port connected by a second hydraulic line to a fluid control device 36. The fluid control device 36 is connected by other hydraulic lines to the front and rear cylinder and piston assemblies 22 and 26.
A fluid schematic drawing for the roll control system 10 is shown in FIG. 2 where components that are similar to components shown in FIG. 1 have the same numerical designators. As shown in FIG. 2, the pump 32 also supplies hydraulic fluid to a power steering valve assembly 52. Indeed, because so many vehicles are equipped with power steering, the power steering pump is typically used to supply pressurized hydraulic fluid to both the power steering valve assembly 52 and the roll control system 10, as shown in FIG. 2. Hydraulic fluid flows from the power steering valve assembly 52 to a pressure differential valve 54 that can establish a pressure differential thereacross to supply pressurized hydraulic fluid to the roll control system fluid control device 36. A check valve 56 prevents back flow of hydraulic fluid from the control device 36 to the power steering valve assembly 52. A relief valve 58 that bypasses the pressure differential valve 54 protects the power steering valve assembly 52 from excessive fluid pressures that may develop in the roll control system 10.
As shown in FIG. 2, the fluid control device 36 includes a three position solenoid actuated control valve 37 that is operative to apply pressurized hydraulic fluid to one side of the pistons contained in the cylinder and piston assemblies 22 and 26 while venting hydraulic fluid from the other side of the pistons. Operation of the control valve 37 causes each of the pistons to move in a selected axial direction within its associated cylinder. As the vehicle is driven along a straight line, the control device 36 is not actuated. When not actuated, as illustrated in FIG. 2, the control valve 37 connects both sides of the pistons directly to the fluid reservoir 34. As a result, the cylinder and piston assemblies 22 and 25 approach equilibrium with the pistons “floating” within their respective cylinders.
During operation of the vehicle, the ECU 12 receives input signals from the wheel speed sensor 14, the lateral accelerometer 16 and the steering angle detector 18. The ECU 12 processes the input signals to determine any roll of the vehicle relative to the wheels 24 and 28. Based upon the determination, the ECU 12 activates the fluid control device 36 to supply pressurized hydraulic fluid to one end of the cylinder and piston assemblies 24 and 26. In response, the pistons move axially within the cylinders to input a torque through the anti-roll bars 20 and 25 to cancel the roll of the vehicle. For example, when the shuttle in the valve 37 is shifted to the right in FIG. 2, the pistons are urged in a downward axial direction. Conversely, when the shuttle is shifted to the left in FIG. 2, the pistons are urged in an upward direction.
Additional details of the roll control system 10 shown in FIGS. 1 and 2 are included in U.S. Pat. No. 5,529,324, which is incorporated herein by reference.